Lithium ion batteries are widely used in portable electronic products such as mobile phones, laptop computers and cameras. Moreover, now, the lithium-ion batteries are also used in hybrid power automobiles. The lithium-ion batteries with high energy are expected to be used for providing electrical power to the electric automobiles. Currently, graphitized carbon negative electrode materials are conventional materials used in the most commercialized lithium-ion batteries because the graphitized carbon negative electrode materials have advantages of low cost and easy control of synthesis processes. However, Carbon negative materials used in the lithium-ion batteries can react during a charging process to form lithium carbides. Due to the instability of the carbon negative materials in an aqueous electrolyte, a conventional lithium-ion battery including a carbon negative material generally employs an organic electrolyte such as a carbonate electrolyte. Thus, during a charging-discharging process, a portion of a reaction product of the organic electrolyte and the carbon negative material covering the surface of the carbon negative material can form a solid-electrolyte interface (SEI) or an interface protective layer (membrane). When the solid-electrolyte interface is relatively dense, the organic electrolyte and the carbon negative material can be effectively isolated, thereby avoiding the further reaction of the organic electrolyte and the carbon negative material. The generation of the solid-electrolyte interface is related to not only the carbon negative material but also the electrolyte (Electrochimica Acta 55 (2010) 6332-6341. In the charging-discharging process, in particular in the charging-discharging process with high output characteristics and at high current, the structure degradation of the carbon (graphite) negative material will occur and the carbon negative material will react with the electrolyte, thereby decreasing the discharge capacity and deteriorating of the cycle performance.
A surface treatment is an effective method to improve the performance of the graphite negative material. The surface treatment is generally to coat the graphite negative material with metal or metal oxide, which is disclosed detailedly by Yuping Wu in his book of Lithium-ion battery—Application and Practic. The surface-modification of the electrode material by the surface treatment plays a positive role. For example, (1) the ion-conductor can be formed on the electrode surface, which contributes to the surface charge transfer; (2) the electrode surface chemical properties can be improved, thereby enhancing the performance of the lithium-ion battery; (3) the surface-modified electrode material can be as the HF removing agent, so as to reduce the acidity of the non-aqueous electrolyte and inhibit the dissolution of metal ions in the positive electrode material; (4) the surface-modified electrode material can has a physical protection layer to prevent a side reaction of the electrode material and the nonaqueous electrolyte. Chinese Patent No. CN 02125138.X discloses a method for preparing a negative active material for a lithium rechargeable battery. The method includes the steps of coating a carbon source with a coating liquid and drying the carbon source, and so on. The coating liquid includes a solute of a coating element source and a solvent of a mixture of an organic solvent and water. Chinese Patent No. CN 200310107365.6 discloses a method for surface-modifying a graphite negative material of a lithium-ion secondary battery by forming oxide film. In the method, graphite powders are immersed into a saturated lithium hydroxide solution containing ethanol to obtain a mixture, and then the mixture is filtered and dried at room temperature under CO2 atmosphere. In the above surface treatment methods, a solid electrolyte interface layer is usually formed on the surface of the graphite negative material. However, the solid electrolyte interface layer can not improve the interlayer structure of the graphite negative material to increase the migration rate of the lithium ions between the graphite layers.